|Publication number||US6946777 B2|
|Application number||US 10/753,613|
|Publication date||Sep 20, 2005|
|Filing date||Jan 8, 2004|
|Priority date||Jan 10, 2003|
|Also published as||US20040201331, WO2004064116A2, WO2004064116A3|
|Publication number||10753613, 753613, US 6946777 B2, US 6946777B2, US-B2-6946777, US6946777 B2, US6946777B2|
|Inventors||Thomas E. Owen|
|Original Assignee||Southwest Research Institute, Gas Research Institute|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (2), Classifications (8), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of U.S. Provisional Application No. 60/439,111, filed Jan. 10, 2003 and entitled “POLYMER FILM COMPOSITE TRANSDUCER”.
The U.S. Government has a paid-up license in this invention and the right in certain circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. DE-FC21-96MC33033 for the U.S. Department of Energy.
This invention relates to piezoelectric transducers, and more particularly to a composite piezoelectric polymer film transducer.
Composite piezoelectric transducers are recognized for their improved performance characteristics in acoustic and ultrasonic applications that require wide bandwidth and high sensitivity. In particular, composite transducer technology can provide significantly higher effective piezoelectric material coefficients than are available in conventional piezoceramic materials. Inherent advantages associated with composite transducer devices include lower acoustical impedence and higher coupling efficiency in the sound propagation medium, specifically, in water, air, and other gaseous media.
One form of piezoelectric composite transducer consists of piezoelectric rods, tubes, or rectangular bars oriented parallel to one another but spaced apart so as to be surrounded and bounded together by an epoxy matrix filler. This composite arrangement may be formed in the shape of a square or rectangular plate or a circular disk whose sound-radiating face is the surface of the plate or disk. The embedded piezoceramic elements are oriented perpendicular to the sound radiating face.
Another form of composite piezoelectric transducer is comprised of piezoceramic plates having a rectangular shape arranged parallel to one another but separated by epoxy bonding layers. This laminated composite array of piezoceramic plates and epoxy layers forms a square or rectangular plate whose sound-radiating face is the surface of the plate. The edges of the piezoceramic plates are oriented perpendicular to the sound-radiating face.
In the first described composite transducer, the cross-axis polarization piezoelectric coefficients of the piezoceramic material govern the acoustical operation. The piezoceramic rods are usually polarized along their length axis (oriented perpendicular to the radiating face). Improved performance characteristics are achieved by the lateral volume expansion and contraction of the piezoceramic elements acting on the surrounding epoxy matrix, giving rise to displacements and sound radiation normal to the face.
In the second described composite transducer, the plates are usually polarized in their thickness dimension (oriented parallel to the radiating face). Their parallel polarization piezoelectric coefficient governs the acoustical operation by applying lateral volume expansion and contraction to the surrounding epoxy matrix. This results in displacements and sound radiation normal to the face of the plate.
The following invention is directed to a composite piezoelectric film transducer for efficient acoustic coupling in air and other gas media. It is capable of providing wide bandwidth and high sensitivity in the sonic and ultrasonic frequency ranges.
An example of an application for the transducer is for precision quantitative measurement of diluent gases, such as nitrogen and carbon dioxide, in natural gas mixtures. It may be further used to accurately measure the speed of sound in such gas mixtures.
Film 31 is backed by a layer 33 of thin inert insulating material, such as a plastic. Specifically, an elastomer material could be used for layer 33. An example of a suitable material for layer 33 is a soft silicon rubber material such as Sylgard 182 ™ material.
As this multi-layered ribbon is wound, it builds up a multi-layer structure with an insulating layer 33 between the active layers of piezolectric film 31. The layered structure comprising ribbon-wound piezoelectric element 101 is analogous to the rectangular plate configuration described in the Background. However, it contains many more layers of piezoelectric and elastomer material. Also, the electroded surfaces 31 b of film 31 are continuous, thereby requiring electrical connections at only two points on piezoelectric element 101.
Film layer 31 a can be any one of various piezoelectric polymer film materials, such as polyvinylidene difluoride, often referred to as PVF2 or PVDF. The use of these materials has the effect of significantly reducing the elastic moduli of the active material, as compared with that of composite transducers using ceramic materials. The result is improved acoustic impedance matching into liquid or gaseous sound propagation media. With improved impedance matching, the self-resonance effects within the transducer structure are also damped, thereby providing wider bandwidth than that obtained with piezoceramic composite transducers.
Referring again to
Once the film comprising piezoelectric element 101 is wound, its expansion and contraction results in expansion and contraction of the diameter of element 101. However, this radial expansion and contraction of element 101 also results in decrease and increase in the thickness of element 101. In other words, element 101 maintains a constant volume as it expands and contracts. Referring to
Because of the expansion and contraction of piezoelectric element 101, transducer 100 has a “thickness” mode resonance associated with the thickness dimension of the sound-radiating plate 103. This dimension corresponds to the width of the film 32. The fundamental resonance of transducer 100 will occur when the width of the film 32 is one-half the wavelength in the composite material. Because the compressional wave velocities in layer 31 and layer 33 are approximately 2,200 meters per second and 1,100 meters per second, respectively, the effective velocity in the composite may be assumed to be approximately the mean value, 1,650 meters per second (65,000 inches per second). Thus, the fundamental resonance frequency of transducer 100 is:
where w is the width of the ribbon. A transducer 100 having a ribbon width of 1 inch will have a resonance frequency of 32.5 kHz. A transducer 100 having a ribbon width of 0.1 inch will have a resonance frequency of 325 kHz. The transducer Q at resonance is:
which, for an estimated value of Qresonance=1, the bandwidth of the transducer will be equal to the resonance frequency. That is, the half-power frequency response of the 1 inch ribbon transducer will be 16,250 to 48,750 Hz and that of the 0.1 inch ribbon transducer will be 162.5 to 487.5 kHz.
If transducer 100 is firmly bonded onto a rigid backing 104, such as a disk of silicon nitride ceramic, the resonance frequency expressed in the above equation will be halved and the resulting transducer Q will be slightly increased. Transducer 100 has a wide bandwidth and is capable of accurately producing sound wave signals that closely correspond to the electrical excitation waveforms applied to the terminals of transducer 100, including fast rise time pulses and broad bandwidth frequency-sweep signals.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7795785 *||Aug 12, 2008||Sep 14, 2010||Murata Manufacturing Co., Ltd.||Ultrasonic sensor|
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|U.S. Classification||310/334, 310/800|
|Cooperative Classification||Y10S310/80, H04R17/00, H04R17/005|
|European Classification||H04R17/00, H04R17/00B|
|Mar 24, 2004||AS||Assignment|
Owner name: UNITED STATES DEPARTMENT OF ENERGY, DISTRICT OF CO
Free format text: CONFIRMATORY LICENSE;ASSIGNOR:SOUTHWEST RESEARCH INSTITUTE;REEL/FRAME:015123/0336
Effective date: 20040212
|Jun 18, 2004||AS||Assignment|
Owner name: SOUTHWEST RESEARCH INSTITUTE, TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:OWEN, THOMAS E.;REEL/FRAME:015493/0910
Effective date: 20040507
|Aug 1, 2005||AS||Assignment|
Owner name: GAS RESEARCH INSTITUTE, ILLINOIS
Free format text: JOINT ASSIGNMENT (50% CONVEYANCE);ASSIGNOR:SOUTHWEST RESEARCH INSTITUTE;REEL/FRAME:016323/0983
Effective date: 20050722
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